Wide band delay line

ABSTRACT

A triangulation-correlation system having an improved correlator using a wide range variable delay line and a multiplier capable of multiplying the wise band signals together.

[5 6] References Cited UNITED STATES PATENTS 3,154,778 10/1964 Kock235/181 X 3,212,091 10/1965 Bissett et a1 343/112 OTHER REFERENCES1.R.E. Dictionary of Electronic Terms and Symbols, 1961, page 116. TR7804 IS. copy in Group Primary Examiner-Rodney D. Bennett, Jr. AssistantExaminer--- Richard E. Berger Att0rr1eys-J. P. Dunlavey and J. O.Tresansky ABSTRACT: A triangulation-correlation system having animproved correlator using a wide range variable delay line and amultiplier capable of multiplying the wise band signals together.

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/5 DELAY /7 GENERATOR 6 GATE W EQQ I J, I DETECTOR QT. .7" in 53RAMPLIFIER i LIMITER 1 PRF 2/ GENERATOR l l .24 {/3 I DETECTOR /5 l 2.4.2 4 4 3 7 M DELAY ,DEFERENTI OR [DIFFEREN IATOR I FLIP FLOP GENERATORT1 FGATE i GATE 2 1+ 1 OUTPUT ATTORNEY WIDE BAND lDlElLAY LINE Thepresent invention relates in general to passive target locating systemsand more particularly to a signal correlator for use in a ghost-freetriangulatiomcorrelation (Tricor) system.

Several methods of target location have been proposed to date. In thewell-known triangulation method, targets are located passively bypointing two radar receivers at the target from different locations.Knowing the distance between the radar receivers and the angle whichthey are pointing, the target is located at the intersection of the twobeams. The resolution of this system is limited by the antenna patternsof the two radar receivers and is hopelessly confused by ghosts whenmore than one target is involved.

The triangulation-correlation system was proposed to solve the ghostproblem presented in the earlier system. This system solves the ghostproblem of triangulation by the introduction of target resolution inpath length difference as well as angle.

The time delay between reception of a signal at the master station alonga direct path from the target and the reception of the signal along asecond path through a repeater station defines a hyperboloid ofrevolution on which the target is located. The intersection of one radarreceiver pointing angle with this hyperboloid locates the target. Thetime delay itself is measured by correlation of signals received alongthe two paths after the signal from the shorter path has been delayedlocally the proper amount.

It is a principal object of the instant invention to provide means forcorrelating the signals in a passive target locating system of thetriangulation-correlation type.

Another object of the invention is the provision of a correlator of thetype described having a variable delay line and a frequency multiplier.

These and other objects and many of the attendant advantages of thisinvention will be readily appreciated as the same becomes betterunderstood by reference to following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram of the detection system according to the invention;

FIG. 2 is a block diagram ofa delay device as used in the invention; and

FIG. 3 is a block diagram of the novel correlator according to theinvention.

The present invention is designed for use with an advanced ghost-freeversion of a triangulation-correlation target locating system known asTricor. This system was designed to operate in conjunction withfrequency diversity radar systems to detect and locate wide-band noisefrom a barrage jammer which might be used against such radars.

There are two important components of a correlator which are influencedby the wide bandwidth requirement of the system. These are (1) a delayline variable in length over the possible ranges to be expected withminimum increments of delay no greater than the resolution of thesystem, and (2) a multiplier capable of multiplying the wide-bandsignals together.

FIG. 11 shows a diagram of the antenna receiving system. The range ofvalues of delay required from the delay line can be calculated asfollows:

1* where C is the velocity of propagation of microwave energy in air.From this representation for the delay it is seen that for Onear dE1/C(2D,), and

for 6near 180, d '50. The delay line should be variable in length, then,over a range from near zero microseconds to l/C(2D microseconds. For aDlof miles, the maximum delay required would be nearly 120 microsecondsor 120,000 feet. For a SO-megacycle bandwidth system, the smallestincrement of delay should be no greater than 0.02 microseconds or feet.These requirements are well beyond the state of the art of conventionaldelay lines which depend on propagation time through a certain distancein a given medium. However, for noise correlation systems, it ispossible to achieve the desired delay line characteristics.

According to the invention the desired delay is achieved by sampling thenoise and then storing the samples a desired length of time before theyare used. This technique can be used with Gaussian noise withno loss ininformation since a sampled Gaussian function is still Gaussian. What islost in a sampled system over a continuous system is time.

Referring to FIG. 2, there is illustrated a delay device according tothe invention. Wide-band microwave noise is received by a receiver 1 andpassed on to a video detector 2. The output of video detector 2 isconnected to a gate 3 which is controlled by a pulse generator 41. Theoutput of the gate 3 controls a boxcar 5 which applies its output to asecond gate 6. Both of the gates 3 and 6 respond to signals from thepulse generator 4, however, the signals to the gate 6 first pass througha delay generator 7. The output of thegate 6 is a pulse identical to thepulse out of the gate 3 except that it is delayed in time. The delay isset by the delay generator 7. Conventional pulse delay generators areavailable which can produce variable delays ranging from zero tothousands of microseconds.

The complete correlator according to the invention is shown in FIG. 3. Asignal from a target station T is picked by the receiver 10 of themaster station and is successively applied to a detector 11 and alimiter 12. The signal is then sampled by a 0.02-microsecond gate 131and stored in a flip-flop 114. The flip-flop 14 has parallel outputswith zero volts on the unexcited leg and suitable positive voltage onthe excited leg. After a time set by a time delay generator 15, a 0. 02microsecond pulse is produced on the flip-flop leg which is excited.This pulse gates a sample of the signal from a repeater station 17, 18after it has been detected and differentiated. Both the gate 113 and thedelay generator 15 operate in response to pulses from the timinggenerator 16.

The repeater station picks up its signal at a receiver 17 and relays itto the master station via a transmitter 18 where it is received andamplified by an RF amplifier 19. The signal is then applied to a+detector 20 and a detector 21. The delayed signal in the master stationis limited by a hardlimiter 12 to two possible values which can benormalized to +1 and l. The multiplication process then reduces tomultiplying the undelayed signal by +1 or l. Multiplication by +1 isaccomplished by gating the output of the +detector 20 and multiplicationby -l is accomplished by gating the output of the -detector 21.

The output of the flip-flop 14 is applied to a pair of gates 22 and 23which are controlled by the delay generator 15. The gates 22 and 23, inturn, control a second pair of gates 24 and 25, respectively, in theoutput of the detectors 20 and 21. The output of the detectors 20 and 21is applied to a pair of differentiators 26 and 27, respectively, andthen passed through the gates 24 and 25 to a summing circuit 28. Theoutput of the summing circuit is integrated in a wave shaper 29 and isthen passed from the correlator to suitable display apparatus (notshown).

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A correlator for a a first receiver for receiving a first group ofreflected radio signals from said target,

a second receiver for receiving a second delayed target, of

radio signals from said target.

a limiter operably connected to receive as input the signals received bysaid first receiver storage means,

means for gating the output of the limiter at timed intervals into saidstorage means.

passive target locating system, comprissaid means releasing the outputfrom said storage means after a predetermined delay, and means forproviding output signals indicative of coincidence between outputsignals from said storage means and output signals from said secondreceiver.

2. A correlator as recited in claim 1, wherein said storage meansincludes a flip-flop.

3. In a correlator for a passive target locating system, a delayapparatus including a receiver,

a video detector connected with the receiver,

a gate connected to the video detector,

a pulse generator connected to the gate,

said pulse generator controlling said gate,

a second gate,

a boxcar connected between the first and second gates, and

a delay generator connected to the pulse generator and between thegates,

said delay generator delaying in time an output pulse from the secondgate.

4. In a passive target locating system including a master station, atarget station, and a repeater station, a correlator including areceiver for picking up a signal from the target station,

a detector connected to the receiver,

a limiter connected to the detector,

a gate connected to the limiter for sampling the signal from thelimiter,

signal storage means connected with the gate,

said storage means having parallel outputs,

a gate connected to each of said outputs,

means for receiving a signal from the repeater station, said repeaterstation comprising a transponder,

means at the master station for amplifying the signal from thetransponder,

detecting means connected to said last-mentioned means,

differentiating means connected to said detecting means,

gating means connected to the differentiating means,

said gating means being connected to said storage means output gates,

summing means connected to the outputs of said gating means and thestorage means output gates, and

integrating means connected to said summing means.

5. A passive target locating system as recited in claim 4,

wherein said signal storage means consists of a flip-flop.

6. A passive target locating system as recited in claim 4,

wherein said signal storage means consists of a flip-flop, and

including a delay generator and a timing generator connected to thefirst mentioned gate.

7. A correlator for a passive target locating system, including a firstreceiver for receiving a first group of radio signals from said target,

a second receiver for receiving a second delayed group of radio signalsfrom said target,

detector means connected to said first receiver for detecting outputsignals therefrom,

storage means having an input adapted to be operably connected to saiddetector means to receive said detected signals from said firstreceiver;

gating means operably connected between the input of said storage meansand said detector means for gating input signals into said storage meansfrom said detector means at timed intervals, and connected to the outputof said storage means for releasing output signals therefrom after apredetermined delay, and

means for providing output signals indicative of coincidence betweenoutput signals from said storage means and output signals from saidsecond receiver.

8. The invention as recited in claim 7, wherein said storage meanscomprises a boxcar.

1. A correlator for a passive target locating system, comprising, afirst receiver for receiving a first group of reflected radio signalsfrom said target, a second receiver for receiving a second delayedtarget, of radio signals from said target. a limiter operably connectedto receive as input the signals received by said first receiver storagemeans, means for gating the output of the limiter at timed intervalsinto said storage means, said means releasing the output from saidstorage means after a predetermined delay, and means for providingoutput signals indicative of coincidence between output signals fromsaid storage means and output signals from said second receiver.
 2. Acorrelator as recited in claim 1, wherein said storage means includes aflip-flop.
 3. In a correlator for a passive target locating system, adelay apparatus including a receiver, a video detector connected withthe receiver, a gate connected to the video detector, a pulse generatorconnected to the gate, said pulse generator controlling said gate, asecond gate, a boxcar connected between the first and second gates, anda delay generator connected to the pulse generator and between thegates, said delay generator delaying in time an output pulse from thesecond gate.
 4. In a passive target locating system including a masterstation, a target station, and a repeater station, a correlatorincluding a receiver for picking up a signal from the target station, adetector connected to the receiver, a limiter connected to the detector,a gate connected to the limiter for sampling the signal from thelimiter, signal storage means connected with the gate, said storagemeans having parallel outputs, a gate connected to each of said outputs,means for receiving a signal from the repeater station, said repeaterstation comprising a transponder, means at the master station foramplifying the signal from the transponder, detecting means connected tosaid last-mentioned means, differentiating means connected to saiddetecting means, gating means connected to the differentiating means,said gating means being connected to said storage means output gates,summing means connected to the outputs of said gating means and thestorage means output gates, and integrating means connected to saidsumming means.
 5. A passive target locating system as recited in claim4, wherein said signal storage means consists of a flip-flop.
 6. Apassive target locating system as recited in claim 4, wherein saidsignal storage means consists of a flip-flop, and including a delaygenerator and a timing generator connected to the first mentioned gate.7. A correlator for a passive target locating system, including a firstreceiver for receiving a first group of radio signals from said target,a second receiver for receiving a second delayed group of radio signalsfrom said target, detector means connected to said first receiver fordetecting output signals therefrom, storage means having an inputadapted to be operably connected to said detector means to receive saiddetected signals from said first receiver; gating means operablyconnected between the input of said storage means and said detectormeans for gating input signals into said storage Means from saiddetector means at timed intervals, and connected to the output of saidstorage means for releasing output signals therefrom after apredetermined delay, and means for providing output signals indicativeof coincidence between output signals from said storage means and outputsignals from said second receiver.
 8. The invention as recited in claim7, wherein said storage means comprises a boxcar.